From 0e43bd7b56f043d08ed3154ce31bb7f07effaebe Mon Sep 17 00:00:00 2001
From: jenskdsgn <jenskdsgn@users.noreply.github.com>
Date: Wed, 3 Apr 2024 08:08:44 +0200
Subject: [PATCH] Fix precision loss due to JSON float parsing (#129)

---
 .../clickhouse/schema_statements.rb                 |  8 ++++++--
 .../add_sample_data/1_create_sample_table.rb        |  1 +
 spec/single/model_spec.rb                           | 13 +++++++++++++
 3 files changed, 20 insertions(+), 2 deletions(-)

diff --git a/lib/active_record/connection_adapters/clickhouse/schema_statements.rb b/lib/active_record/connection_adapters/clickhouse/schema_statements.rb
index d7a3386d..a3be9e7c 100644
--- a/lib/active_record/connection_adapters/clickhouse/schema_statements.rb
+++ b/lib/active_record/connection_adapters/clickhouse/schema_statements.rb
@@ -233,11 +233,11 @@ def format_body_response(body, format)
         end
 
         def format_from_json_compact(body)
-          JSON.parse(body)
+          parse_json_payload(body)
         end
 
         def format_from_json_compact_each_row_with_names_and_types(body)
-          rows = body.split("\n").map { |row| JSON.parse(row) }
+          rows = body.split("\n").map { |row| parse_json_payload(row) }
           names, types, *data = rows
 
           meta = names.zip(types).map do |name, type|
@@ -252,6 +252,10 @@ def format_from_json_compact_each_row_with_names_and_types(body)
             'data' => data
           }
         end
+
+        def parse_json_payload(payload)
+          JSON.parse(payload, decimal_class: BigDecimal)
+        end
       end
     end
   end
diff --git a/spec/fixtures/migrations/add_sample_data/1_create_sample_table.rb b/spec/fixtures/migrations/add_sample_data/1_create_sample_table.rb
index 699c4da7..9619bfe5 100644
--- a/spec/fixtures/migrations/add_sample_data/1_create_sample_table.rb
+++ b/spec/fixtures/migrations/add_sample_data/1_create_sample_table.rb
@@ -11,6 +11,7 @@ def up
       t.datetime :datetime64, precision: 3, null: true
       t.string :byte_array, null: true
       t.uuid :relation_uuid
+      t.decimal :decimal_value, precision: 38, scale: 16, null: true
     end
   end
 end
diff --git a/spec/single/model_spec.rb b/spec/single/model_spec.rb
index 88c9d54a..e9e46b54 100644
--- a/spec/single/model_spec.rb
+++ b/spec/single/model_spec.rb
@@ -180,6 +180,19 @@ class ModelPk < ActiveRecord::Base
       end
     end
 
+    describe 'decimal column type' do
+      let!(:record1) do
+        Model.create!(event_name: 'some event', decimal_value: BigDecimal('95891.74'))
+      end
+
+      # If converted to float, the value would be 9589174.000000001. This happened previously
+      # due to JSON parsing of numeric values to floats.
+      it 'keeps precision' do
+        decimal_value = Model.first.decimal_value
+        expect(decimal_value).to eq(BigDecimal('95891.74'))
+      end
+    end
+
     describe '#settings' do
       it 'works' do
         sql = Model.settings(optimize_read_in_order: 1, cast_keep_nullable: 1).to_sql